Abstract

A combination of online and offline mass spectrometric techniques was used to characterize the chemical composition of secondary organic aerosol (SOA) generated from the photooxidation of α-pinene in an atmospheric simulation chamber. The filter inlet for gases and aerosols (FIGAERO) coupled with a high-resolution time-of-flight iodide chemical ionization mass spectrometer (I–ToF-CIMS) was employed to track the evolution of gaseous and particulate components. Extracts of aerosol particles sampled onto a filter at the end of each experiment were analyzed using ultra-performance liquid chromatography ultra-high-resolution tandem mass spectrometry (LC-Orbitrap MS). Each technique was used to investigate the major SOA elemental group contributions in each system. The online CIMS particle-phase measurements show that organic species containing exclusively carbon, hydrogen and oxygen (CHO group) dominate the contribution to the ion signals from the SOA products, broadly consistent with the LC-Orbitrap MS negative mode analysis which was better able to identify the sulphur-containing fraction. An increased abundance of high carbon number (nC ≥ 16) compounds additionally containing nitrogen (CHON group) was detected in the LC-Orbitrap MS positive ionisation mode, indicating a fraction missed by the negative mode and CIMS measurements. Time series of gas-phase and particle-phase oxidation products provided by online measurements allowed investigation of the gas-phase chemistry of those products by hierarchical clustering analysis to assess the phase partitioning of individual molecular compositions. The particle-phase clustering was used to inform the selection of components for targeted structural analysis of the offline samples. Saturation concentrations derived from near-simultaneous gaseous and particulate measurements of the same ions by FIGAERO-CIMS were compared with those estimated from the molecular structure based on the LC-Orbitrap MS measurements to interpret the component partitioning behaviour. This paper explores the insight brought to the interpretation of SOA chemical composition by the combined application of online FIGAERO-CIMS and offline LC-Orbitrap MS analytical techniques.

Highlights

  • Secondary organic aerosol (SOA) makes a significant contribution to atmospheric aerosols, which have an important influence on climate and adverse impact on human health and air quality (Nel, 2005; Kroll and Seinfeld, 2008; Hallquist et al, 2009)

  • This paper explores the insight brought to the interpretation of secondary organic aerosol (SOA) chemical composition by the combined application of online FIGAERO-CIMS and offline LC-Orbitrap MS analytical 45 techniques

  • The purpose of this paper is to explore the benefits of combinatorial LC-Orbitrap MS and 115 FIGAERO-CIMS analytical techniques to investigate SOA chemical composition, demonstrating the power of this combination from a technical perspective

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Summary

Introduction

Secondary organic aerosol (SOA) makes a significant contribution to atmospheric aerosols, which have an important influence on climate and adverse impact on human health and air quality (Nel, 2005; Kroll and Seinfeld, 2008; Hallquist et al, 2009). As a result of the various VOCs involved and the complexity of the oxidation 60 processes, oxidation products span a wide range of molecular composition and physiochemical properties (Ma et al, 2008; Laj et al, 2009; Mentel et al, 2015; Mutzel et al, 2015; Mohr et al, 2019). Such chemical complexity poses a major challenge in the molecular characterization of SOA

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